Norepinephrine stimulates M2 macrophage polarization via β2-adrenergic receptor-mediated IL-6 production in breast cancer cells.

Previous studies have demonstrated that norepinephrine (NE) released during chronic stress promotes breast cancer (BC) metastasis via adrenergic receptors (ARs). However, the effect of NE on tumor-associated macrophage polarization and the underlying mechanisms remain largely unknown. In this study, we aimed to investigate the influence of NE on M2 macrophage polarization, with a particular focus on the crosstalk between macrophages and BC cells. Our results demonstrated that, although NE alone did not directly induce the expression of M2 macrophage markers, conditioned medium from NE-treated MDA-MB-231 human BC cells (NE CM) significantly promoted M2 macrophage polarization in THP-1 macrophages. We found that NE stimulated IL-6 production in MDA-MB-231 cells via β2-AR/NF-κB pathway, which activated STAT3 in THP-1 cells to induce M2 macrophage polarization. NE failed to induce IL-6 production and NF-κB activation when ADRB2 was knocked down in MDA-MB-231 cells. Furthermore, ADRB2 knockdown in cancer cells suppressed NE CM-induced M2 macrophage polarization, as well as M2 macrophage-induced cancer cell migration. Taken together, our results suggest that NE stimulates M2 macrophage polarization by inducing IL-6 secretion from BC cells through a β2-AR-dependent mechanism, which subsequently promotes cancer cell migration. Targeting β2-AR may represent a promising strategy to prevent chronic stress-induced BC metastasis.